14/02/2026
Soooooo important in rehab - posterior chain!!! Get the dominance right!
๐ง๐ต๐ถ๐ด๐ต ๐ ๐๐๐ฐ๐น๐ฒ ๐๐ต๐ฎ๐ป๐ด๐ฒ๐ ๐ถ๐ป ๐๐ต๐ฒ ๐๐๐-๐๐ฒ๐ณ๐ถ๐ฐ๐ถ๐ฒ๐ป๐ ๐๐ป๐ฒ๐ฒ: ๐ 4-๐ฌ๐ฒ๐ฎ๐ฟ ๐๐ผ๐ป๐ด๐ถ๐๐๐ฑ๐ถ๐ป๐ฎ๐น ๐ ๐ฅ๐ ๐ฆ๐๐๐ฑ๐ ๐ผ๐ณ 1,207 ๐ฃ๐ฎ๐๐ถ๐ฒ๐ป๐๐
๐ฆต The anterior cruciate ligament (ACL) serves as a fundamental mechanical and sensory stabilizer of the knee. ACL tears are among the most prevalent ligamentous injuries, with an annual U.S. incidence of 68.6 per 100,000 (https://pubmed.ncbi.nlm.nih.gov/26920430/). While much of clinical orthopaedics has traditionally focused on acute quadriceps weakness following injury, emerging evidence suggests that the long-term neuromuscular landscape is far more complex. Systematic reviews, such as those by Birchmeier et al. (2020, https://pubmed.ncbi.nlm.nih.gov/31608490/) and Schwartz et al. (2025, https://pubmed.ncbi.nlm.nih.gov/39800896/), have highlighted persistent strength deficits and muscle size alterations that remain even years after the initial trauma. This suggests that an ACL tear is not merely a structural failure but a catalyst for chronic, systemic adaptations in the lower limb.
๐ A brand-new longitudinal matched-cohort study by Alzobi and colleagues (https://pubmed.ncbi.nlm.nih.gov/41370366/), utilizing data from the Osteoarthritis Initiative (OAI), tracked 1,207 participants over a four-year period to observe how an unreconstructed ACL tear influences thigh muscle morphology and function. The researchers employed a deep-learning U-Net model to segment MRI data, allowing for precise quantification of muscle cross-sectional area (CSA) and intramuscular adipose tissue (IMAT).
๐ ๐๐ฒ๐ ๐๐ถ๐ป๐ฑ๐ถ๐ป๐ด๐
Contrary to the common clinical emphasis on the quadriceps, this study revealed that the most significant long-term deterioration occurs in the posterior thigh:
1๏ธโฃ ๐ฆ๐ฒ๐น๐ฒ๐ฐ๐๐ถ๐๐ฒ ๐๐๐ฟ๐ผ๐ฝ๐ต๐: ACL-deficient thighs experienced progressive atrophy in the hamstrings (-28.18 mm/year) and the sartorius (-3.02 mm/year).
2๏ธโฃ ๐ค๐๐ฎ๐ฑ๐ฟ๐ถ๐ฐ๐ฒ๐ฝ๐ ๐๐ฆ๐ ๐ฆ๐๐ฎ๐ฏ๐ถ๐น๐ถ๐๐: Surprisingly, no significant longitudinal changes were observed in quadriceps or adductor CSA over the four-year window.
3๏ธโฃ ๐๐๐ป๐ฐ๐๐ถ๐ผ๐ป๐ฎ๐น ๐๐ฒ๐ฐ๐น๐ถ๐ป๐ฒ: Corresponding with the physical atrophy, hamstring strength decreased significantly (-3.49 N/year), while quadriceps force remained relatively stable.
4๏ธโฃ ๐ ๐๐๐ฐ๐น๐ฒ ๐ค๐๐ฎ๐น๐ถ๐๐: There were no significant differences in fat infiltration (IMAT) or contractile percentage between ACL-deficient and ACL-intact groups, suggesting the primary issue is muscle volume rather than "marbling" of the tissue.
๐ก ๐๐น๐ถ๐ป๐ถ๐ฐ๐ฎ๐น ๐๐บ๐ฝ๐น๐ถ๐ฐ๐ฎ๐๐ถ๐ผ๐ป๐
The results suggest that the loss of the ACL-hamstring reflex arcโa feedback loop where ACL mechanoreceptors trigger hamstring activation (https://pubmed.ncbi.nlm.nih.gov/3618871/, https://pubmed.ncbi.nlm.nih.gov/11206261/)โmay lead to chronic disuse and subsequent wasting of the posterior muscles. This "quadriceps dominance" can further destabilize the knee by increasing anterior tibial shear. These findings challenge the traditional "quad-centric" view of ACL recovery. To protect the long-term health of the knee, rehabilitation must evolve to include rigorous, targeted strategies for hamstring preservation.
